37S PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
{T. gigcis). By taking his original diagnosis and the characters 
shown in his fig. 69 of the type, it is clear that the genus is distin- 
guished by the following combination of characters : 
Atrial languet present; four rows of branchial stigmata; sperm duct 
spirally coiled about the testis, testis not divided. 
In all characters except the last, the species described below would 
agree with this diagnosis. It has, however, the testis divided into two 
parts. Division to this limited extent has not usually been treated as of 
sufficient importance to a\ arrant the establishment of a distinct genus, 
so that the writer would modify the above diagnosis by adding the 
qualification "into more than two distinct parts" to the last statement 
thereof. Should at some future time more information about Delia 
Valle's type be forthcoming and prove that the inclusion of this species 
in Tetradidemnum is not justifiable, it will then be soon enough to 
burden the nomenclature of this group with a new generic name. 
Tetradidemnum albidum (Verrill). 
Text-figs. 13, U, 15; PI. 35, fig. 2; PI. 39, fig. 13. 
1851. Didemnum roseum + Leptodinum gelatinosum Sars, Nyt. Mag. Nat- 
urvidensk., vol. 6, pp. 153, 154. 
1858. Didemnum roseum + Leptoclinum gelatinosum Sars, Forh. Mdenskabs- 
Selsk. Christiania, p. 66. 
1867. Didemnium roseum Packard, Mem. Boston Soc. Nat. Hist., vol. 1, 
. p. 276. 
1870. Didemnium roseum Binney, Gould's Invertebrata of Massachusetts, 
ed. 2, p. 4. 
1870. Didemni<m roseum Dall, Proc. Boston Soc. Nat. Hist., vol. 13, p. 255. 
1871. Leptoclinum albidum (part.) -I- Leptoclinum luteolum (part.) Verrill, 
Amer. Journ. Sci., ser. 3, vol. 1, p. 446. 
1872. Leptoclinum albidum (part.) -I- Leptoclinum luteolum (part.) Verrill, 
Amer. Journ. Sci., ser. 3, vol. 3, pp. 212, 213. 
1873. Leptoclinum albidum (part.) + Leptoclinum luteolum (part.) Verrill 
and Smith, Report on Invertebrate Animals of Vineyard Sound, pp. 
403 (411, 424), 705, 706. 
1873. ? Didemnum roseum Ehlers, Sitz.-Ber. phys.-med. Soc. Erlangen, no. 5, 
p. 7. 
1874. Leptoclinum albidum + Leptoclinum luteolum Verrill, Amer. Journ. 
Sci., ser. 3, vol. 7, pp. 39. 43, 413, 504. 
1874. Leptoclinum albidum + Leptoclinum luteolum A'errill, Proc. Amer. 
Assoc. Adv. Sci., vol. 22, pp. 352, 355, 359, 363. 
1879. Leptoclinum cdbidum (part.) + L. albidum var. luteolum (part.) Verrill, 
Preliminary Check-list of Marine Invertebrata, p. 27. 
